Release 13 of the Third Generation Partnership Project (3GPP) supports Licensed Assisted Access (LAA) in downlink. 3GPP has implemented a mandatory Listen Before Talk (LBT) mechanism for LAA evolved Node Bs (eNodeBs or eNBs) based on energy detection methods to be able to use the unlicensed channel and co-exist with WiFi access points (APs). At the user equipment (UE) side, the UE has to continuously monitor for the physical downlink control channel (PDCCH) containing the downlink control information (DCI) because the UE is unaware of the eNB's transmission opportunities. The DCI contains vital resource assignments intended for the UE.
Both of these situations, i.e. the energy detection at the eNB and the PDCCH monitoring at the UE, are power intensive.